Field of the Invention
The present invention relates to a hydraulic system in which a control shaft that alters the volume of a hydraulic rotor is rotated around the axis by rotary power from a drive motor, and to a driving unit including a drive motor that serves as a power source for driving an output shaft, which is a driving target, and a deceleration mechanism that decelerates the rotary power of the drive motor and outputs the decelerated rotary power toward the output shaft.
Related Art
A hydraulic system including a rotational shaft, a hydraulic rotor supported by the rotational shaft so as to be incapable of relative rotation, an output adjuster that varies the volume of the hydraulic rotor, and a control shaft that tilts the output adjuster in accordance with rotation around the axis is widely used as a hydraulic pump system including a hydraulic pump as a hydraulic rotor, a hydraulic motor system including a hydraulic motor as a hydraulic rotor, and a hydrostatic transmission (HST) including a hydraulic pump and a hydraulic motor as hydraulic rotors.
For example, U.S. Pat. Nos. 8,511,216 and 8,517,138 each disclose an HST including an electric motor that serves as a power source for rotating the control shaft around the axis.
This conventional HST includes a deceleration mechanism that decelerates the rotary power of the electric motor and outputs the decelerated rotary power toward the control shaft, and, accordingly, the size of the electric motor can be reduced.
However, the deceleration mechanism in this conventional HST has an electric motor output gear that is fixed to the electric motor output shaft of the electric motor and a sector gear that is fixed to the control shaft and meshes with the electric motor output gear, and is thus problematic in that in order to obtain a sufficient deceleration ratio, the HST increases in size.
That is, in order to obtain a large deceleration ratio with the above conventional configuration, the difference between the pitch diameters of the electric motor output gear and the sector gear has to be increased, and, consequently, the electric motor output shaft needs to be largely displaced from the control shaft in the radial direction with reference to the axis of the control shaft. Accordingly, the conventional HST is problematic in that in order to obtain a sufficient deceleration ratio and reduce the size of the electric motor, the overall size of the HST is increased, especially in the radial direction with reference to the control shaft.